1. Field of the Invention
Methods and systems consistent with the present invention relate to a beacon scheduling in a network system, and more particularly, to beacon scheduling of a router in a network system to prevent a beacon conflict.
2. Description of the Related Art
In a ZigBee network topology, nodes in a network system are divided into a ZigBee coordinator (ZC), a ZigBee router (ZR), and a ZigBee end device (ZE).
The ZC is on the top of a tree structure and responsible for managing the tree. The ZR is below the ZC and responsible for relaying a beacon transmitted from the ZC to its child nodes (i.e., ZEs or other ZRs) so that the tree structure can be expanded.
The ZE is at the bottom of the network topology. The ZE synchronizes using the beacon transmitted from the ZR and the ZC, and performs communications.
To form such a tree structure, ZRs need to relay beacons received from ZCs to their child nodes. At this time, if the transmission point of the beacons is randomly selected by the ZRs, the beacons are subject to collisions at the child nodes. These beacon collisions block the communications between the nodes.
FIG. 1 illustrates a conventional beacon scheduling method. According to ZigBee NWK v.0.92 (02130r9ZB_NWK_Network-Specification V092), in a case that a ZR is connected as a child node to a parent node which regularly transmits beacons throughout the tree topology, the ZR first schedules its beacons transmission by tracking the beacons of the parent node prior to its beacon transmission to its child node, and transmits its beacons by intervals of a beacon transmission (Tx) offset.
FIGS. 2A and 2B illustrate a problem of the conventional beacon scheduling method.
It is assumed that two child nodes (child 1 and child 2) are connected to the same parent node and receive beacons from the parent node but do not know each other in their respective regions.
Referring first to FIG. 2A, since the child 1 and the child 2 cannot track beacons of the other, the same beacon Tx offset may be used based on the beacons of the parent node.
Referring to FIG. 2B, in the hatched area where the coverage of the child 1 and the child 2 overlaps, the beacons from the child 1 and the child 2 collide. As a result, no child node within the overlapping region can receive the beacons from the child 1 and the child 2.